The present invention in general relates to a method of processing a surface of a mold using electric discharge, an electrode used in such processing and a method of manufacturing such an electrode. More specifically, this invention relates to a technology of processing a surface of a mold using a formed electrode.
In molds for forging process, molds for bending process and molds for drawing process, surfaces of these molds must have excellent abrasion resistance properties, in order to achieve a desired perseverance properties. Conventionally, heat processing is mainly performed as the surface processing for imparting abrasion resistance properties to molds. In addition, in some cases, a hard film is coated on the mold surface by the nitriding treatment or the carburizing treatment of the mold surface, or by deposition plating such as CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition) and the like.
However, when the mold surface is treated by the heat processing, the precision of the mold configuration inevitably deteriorates due to shape-change resulted from heating, and cracks tend to be generated in the mold depending on the shape of the mold. As a result, a significant number of failures may be produced in the mold producing process.
On the other hand, in the case of the hard-film coating by thermal refining such as nitriding and carburizing treatments or the deposition plating, various problems, such as too high processing cost, restriction on the size of materials to be processed or the like, arise. Due to this, the hard-film coating is hardly performed for press molds or the like.
As another method of coating a hard film on the mold surface, there has been proposed a discharge surface processing method which includes the steps of: generating pulse-like discharge between an electrode and a work (mold) in a processing liquid such as a discharge processing oil; and forming on the mold surface, by the discharge energy, a hard film composed of the electrode material or a substance like a metal carbide generated by the reaction of the electrode material due to the discharge energy. A discharge surface processing method of this type is disclosed in Japanese Patent Office Application Laid-Open gazettes (JP-A No. 9-19829 and JP-A No. 9-192937).
As is disclosed in Japanese Patent Office Application Laid-Open gazettes (JP-A No. 8-257841), the discharge surface processing can be carried out either by using a simple-shaped electrode having a rod-like shape or by using a formed electrode. When the mold surface is discharge-surface processed by a simple-shaped electrode having a rod-like shape, the discharge surface processing is carried out by the electrode scanning along the mold surface. However, this process is quite time-consuming and not capable of coping with a three-dimensional complicated mold surface. In short, it is difficult to carry out highly precise discharge surface processing by a simple-shaped electrode having a rod-like shape.
On the other hand, in a case in which the mold surface is discharge-surface processed by a formed electrode, it is necessary to prepare an electrode for each mold such that the shape of the electrode corresponds to the corresponding mold, although the aforementioned problems that occur in the case of the simple-shaped electrode having a rod-like shape are avoided.
Conventionally, a formed electrode is produced: by filling metal powder such as Ti, TiH2 in a die for producing a formed electrode; and pressing and compressing the metal powder in the die by a punch, so as to pressure-mold a formed electrode by utilizing solidification of the metal powder resulted from the pressing. A formed electrode produced in such a manner is called a xe2x80x9cformed pressed powder electrodexe2x80x9d.
When a formed pressed powder electrode is produced in such a manner, a die for producing the formed electrode and a punch are required, thereby increasing the production cost. In addition, the precision in producing the die for the formed electrode production and the precision in producing the punch, directly influence the precision in the discharge surface processing of the die surface. Accordingly, unless the punch and the die for producing the formed electrode are produced in a highly precise manner, the discharge surface processing cannot be conducted as precisely as desired.
In particular, when the mold is produced in a relatively small scale, the number of required electrode is not large. In other words, the production cost of the electrode significantly affects the production cost of the mold as a whole, thereby preventing the discharge surface processing from being more widely performed.
The present invention has been contrived in order to solve the problems as described above. It is an object of the present invention to provide a method of processing a surface of a mold using electric discharge which is highly accurate, efficiently and low-cost. It is also an object of the present invention to provide an electrode used in such processing and a method of manufacturing such an electrode.
The method of processing a surface of a mold using electric discharge of the present invention comprises the following steps. That is, preparing a compressed powder formed electrode, and carrying out discharge surface processing of mold surface of the mold by using the compressed powder formed electrode. The compressed powder formed electrode is produced by the following method. That is, filling material powder such as metal powder or metal compound powder in a female mold of the mold to be discharge surface processed, and press-molding the material powder in the female mold by a male mold of the mold.
Thus, the surface of the mold is treated using the compressed powder formed electrode. This electrode is molded by the mold to be dischargexe2x80x94surface processed without using a die and a punch for producing the formed electrode, such that the formed electrode very precisely corresponds, in shape, to the mold surface. As the formed electrode very precisely corresponds, in shape, to the mold surface, the discharge surface processing can be carried out efficiently and very precisely on the mold surface.
Further, the method of processing a surface of a mold using electric discharge of the present invention comprises the following steps. That is, attaching the compressed powder formed electrode to one of the male mold and the female mold with a conductive adhesive, and carrying out the discharge surface processing of the other of the male mold and the female mold, by using the one of the male mold and the female mold itself as an electrode holder.
Accordingly, the compressed powder formed electrode, formed by the mold to be discharge surface processed, is attached to one of the male mold and the female mold by the conductive adhesive, and the discharge surface processing of the other of the male mold and the female mold is carried out by using the one of the male mold and the female mold itself as an electrode holder.
Further, the method of manufacturing an electrode, which electrode is used in processing a surface of a mold, of the present invention comprises following steps. That is, filling material powder such as metal powder, metal compound powder or the like in the female mold of a mold to be discharge surface processed, and press-molding the material powder in the female mold by the male mold of the mold, thereby producing a compressed powder formed electrode.
Accordingly, a compressed powder formed electrode, which very precisely corresponds, in shape, to the mold surface, can be obtained without using a die and a punch for producing the formed electrode.
Further, an electrode, which electrode is used in processing a surface of a mold, of the present invention is formed as follows. That is, attaching the compressed powder formed electrode to one of the male mold and the female mold with a conductive adhesive, and using the one of the male mold and the female mold itself as an electrode holder.
Accordingly, formed electrode formed by the mold to be discharge surface processed, is attached to one of the male mold and the female mold to be discharge surface processed by the conductive adhesive, and the one of the male mold and the female mold itself is used as an electrode holder.
Further, an electrode, which electrode is used in processing a surface of a mold, of the present invention is formed as follows. That is, filling material powder such as metal powder, metal compound powder or the like in the female mold of a mold to be discharge surface processed; and press-molding the material powder in the female mold by the male mold of the mold.
Accordingly, a formed electrode for mold discharge surface processing which very precisely corresponds, in shape, to the mold surface can be produced without using a die and a punch for producing the formed electrode, enabling highly precise mold discharge surface processing.
Further, an electrode, which electrode is used in processing a surface of a mold, of the present invention is formed as follows. That is, the electrode for processing mold discharge surface is attached to one of the male mold and the female mold with a conductive adhesive, and the one of the male mold and the female mold itself is used as an electrode holder.
Accordingly, this formed electrode for mold discharge surface processing is attached, with a conductive adhesive, to one of the male mold and the female mold to be discharge surface processed, and the one of the male mold and the female mold itself is used as an electrode holder.